Business Intelligence projects (like software development projects) are prone to bad or completely absent planning prior to their start. Most of us that work in the technology industries are busy professionals that can never seem to find enough time. When you consider that mindset and then the fact that project planning requires additional time...well you get the point. By our very nature we do not want to waste time!
BI projects are large endeavors, rather BI enterprise projects are large endeavors. Personally, I have been fortunate enough to plan, design, and implement several enterprise systems over the years with some of the best BI professionals. And every time I was glad that my team made a plan!
'Scope Creep' is just as common in BI projects as it is in software development. It is easy to not remain focused through the entire lifecycle of an enterprise BI project. The plan can also serve as a deliverable schedule for your project sponsors (usually executives). In a consulting engagement scenario the importance of planning is of even greater importance as the entire project will be based on deliverables and their scheduling.
While I agree that we hate to waste time, I can tell you that proper planning (for any project) is NOT a waste of time.